In Situ Construction of Single-Site Ti Active Centers on Carbon Nitride for Photocatalytic Chemoselective Hydrogen Transfer Reduction

Abstract

In this work, we report an in situ construction of single-site Ti active centers on a carbon nitride surface during photocatalytic processes for one-pot chemoselective hydrogen transfer reduction of nitroaromatics and domino-type reaction using Cp2TiCl2 and −OH-enriched carbon nitride (OHCN) as precatalysts. Due to the selective adsorption of nitro and the promotion of photogenerated charge transfer by single-site Ti active species and the formation of Ti3+, the system can achieve an efficient chemoselective reduction of nitroaromatics containing various substituents, especially sensitive substituents (CC, CC, CO, CN, CN, C–X (X is halogen), etc.). The two processes of chemoselective reduction of nitroaromatics and oxidation of aromatic alcohols are photocatalytically coupled to form a complete photocatalytic cycle, which allows the simultaneous formation of two high-value-added products, aromatic amines and aromatic aldehydes. More valuable products like imines are obtained by effecting the reduction of the nitro moiety to −NH2 in the presence of aromatic alcohols that can react in a domino-type process. This work guides the in situ preparation of non-noble metallic single-site photocatalysts and provides a strategy for the photocatalytic synthesis of valuable organic compounds from nitroaromatics.

Regulating CO and H2 Ratios in Syngas Produced from Photocatalytic CO2/H2O Reduction by Cu and Co Dual Active Centers on Carbon Nitride Hollow Nanospheres

“…These results can be confirmed by X-ray diffraction (XRD) characterization (Figure S11). The XRD patterns of Co 0.5 /Cu 0.5 -bpy/CNHS, Co 1.0 -bpy/CNHS, and Cu 2.0 -bpy/CNHS show the characteristic diffraction peaks attributed to carbon nitride − but no diffraction peaks of Co and Cu-related nanoparticles and clusters. In addition, we tested the EDX spectrum (Figure S12) and C, N, Co, and Cu element mapping of Co 0.5 /Cu 0.5 -CNHS (Figure b–f).…”

Recent advances on carbon nitride-based photocatalysts for organic transformations in aqueous media

“…The research group of Gao and Gu reported a chemoselective hydrogen transfer reduction of nitroaromatics and a domino-type reaction over the composite (OHCN-Ti) of Cp 2 TiCl 2 and –OH-enriched carbon nitride (OHCN) in the mixed solvent of water and isopropanol (Scheme 4E). 68 Various nitroaromatics with different functional groups such as olefins, alkynes, ketones, imines, and haloaromatics are tolerated in this catalytic system with nitro groups reduced to amines. The remarkable chemoselectivity observed in this reaction was likely due to the preferential coordination ability of oxyphilic titanium with nitro functionality.…”

Carbon nitride based materials: more than just a support for single-atom catalysis

“…327 Zhang et al managed to apply the first non-noble SAC for hydrogen transfer reduction. 559 By utilizing –OH enriched carbon nitrides (OHCN), the authors stabilized Cp 2 TiCl 2 leading to the formation of Ti single-sites Ti/OHCN-g. This catalyst was applied to selectively reduce several nitroaromatics.…”

“…The authors tested a broad scope (38 substrates) and reported successful results, with no yield lower than 78%, demonstrating the robustness of this system. 559…”